Not applicable.
Not applicable.
The invention relates to radiation receivers with a photodetector and a sensor, and also to a method of operating the same, and a rangefinder with such a radiation receiver.
A laser ceilometer with a device for reducing the radiation emitted by the laser ceilometer is known from U.S. Pat. No. 4,288,158. As soon as the direction of the laser ceilometer deviates by more than a predetermined angle from the vertical position, the angle being detected by a sensor, the radiation emitted by the laser ceilometer is reduced. It is thereby ensured that a radiation intensity emitted by the laser ceilometer and by which the human eye could be damaged is no longer emitted as soon as the direction of the laser ceilometer deviates from the vertical position by a predetermined amount whereby the possibility exists that the radiation of the laser ceilometer can enter the human eye.
A method is known from DE 43 25 139 C1 for preventing eye damage during the use of high power lasers. In this method, or with the apparatus known from this document, the radiation of a warning laser is superposed on the radiation of a high power laser. The radiation intensity of the warning laser is increased such that an observer""s eyelid would be excited to close due to the radiation intensity emitted by the warning laser before a radiation intensity dangerous for the observer""s eye is emitted by the high power laser.
A system and a method are known from U.S. Pat. No. 4,552,454, in particular for testing laser rangefinders. In this system for testing laser rangefinders, the radiation emitted by a transmitter is first coupled into a device with reflecting surfaces. The radiation is focused by this device on a ray input of a glass fiber, which is provided centrally and at the end with reflecting surfaces. The radiation is at least partially reflected at these reflecting surfaces and is conducted to a receiver by this system provided with reflecting surfaces. A calibration of the rangefinder can be carried out by means of this arrangement, based on the known path difference between the surfaces provided centrally in the fiber and at the end in the fiber.
Rangefinders are furthermore known which have a laser as the radiation source, the range being determined using the radiation reflected back. For this purpose, a radiation receiver is allocated for the back-reflected radiation.
Since the receiver of the present rangefinders has an extremely small surface, in order to attain a high detection sensitivity, problems of optical destruction occur more and more frequently in the present rangefinders. The receiver surface has a diameter of only just 70 xcexcm in some cases. The receiving optics of such a rangefinder is designed so that the whole of the radiation within the visual field and striking the entrance aperture is collected onto the receiver. Thus even very low radiation powers or radiation densities in the entrance aperture can lead to an optical destruction of the detector. A particular danger arises, in particular, from the high peak pulse power, which can be in the megawatt range, emitted by the rangefinder. Reflections of the transmitted beam at back-reflecting targets situated near to the device, or at targets with a high retroreflected fraction, lead as a rule to destruction of the receiver.
Even the radiation produced in the device itself can lead to destruction of device components due to back-scattering under unfavorable conditions.
The invention has as its object to provide a radiation receiver and a method of operating the same so that a destruction of device components, particularly of the photodetector, by self-radiation and extraneous radiation is prevented.
A further object of the invention is to provide a radiation receiver or a rangefinder with a radiation receiver which is immediately available for measuring operation after a radiation input which is harmful to the radiation receiver.
The object of the invention is attained by a radiation receiver comprising a photodetector, a sensor, a shutter arranged before the photodetector, and a delay device arranged before the shutter. The sensor receives radiation intensity. The shutter is driven in dependence on detected incident radiation intensity. The incident radiation is supplied to the photodetector via the delay device. The object of the invention is also attained by the method for operating the radiation receiver.
By the measure of providing a delay device, it can be ensured that a shutter arranged before the radiation receiver is closed before the radiation incident on the radiation receiver can pass the shutter and reach the photodetector unhindered. A sensor is provided for the determination of the radiation intensity of the incident radiation, and is arranged such that as rapid as possible closing of the shutter can be attained.
It has been found to be advantageous for the determination of the radiation intensity to couple out a fraction, preferably less than 5%, of the incident radiation and to conduct it to the sensor. A beamsplitter has been found to be particularly advantageous for the coupling-out.
If the incident radiation is coupled into an optical fiber, particularly by means of a convergent optics, a fiber branch can be used for branching off a fraction of the radiation intensity. The use of optical fibers is advantageous because distortion due to objects intruding laterally into the beam path is prevented and it is easy to conduct the radiation on a non-linear path, thus giving space-saving advantages.
It has been found to be advantageous to provide an optical fiber as a delay device. In such optical fibers, radiation can be conducted with small losses. It is also possible to arrange an optical fiber in a curved shape without incurring considerable radiation losses. The radiation can thus be conducted in the optical fiber with small losses. The possibility of conducting the radiation on curved paths contributes greatly to the compactness of the radiation receiver.
It has been found to be advantageous to use a shutter, which has an electro-optical substance. Such electro-optical substances, such as e.g. liquids and particularly crystals, rapidly change their optical properties when an applied potential is changed and thus have an outstandingly short reaction time.
It has been found to be advantageous to provide a shutter, which includes a filter with variable absorption properties, or several filters with different absorption properties. It is thereby possible to damp the incident radiation in dependence on the detected radiation intensity by means of the shutter or by selection of the corresponding shutter, so that the radiation reaching the photodetector does not exceed the maximum permissible intensity. By feedback of information from the shutter to an evaluation electronics allocated to the photodetector, the degree of damping effected by the shutter can be taken into account by the evaluation of the obtained data. The range of use of the radiation receiver can thereby be considerably enlarged.